This invention relates to a voltage converter system of the general type disclosed in Means U.S. Pat. No. 3,665,502. One of the embodiments disclosed in that patent comprises a motor-alternator set having a dc. motor energizable from a battery and having an alternator which produces an ac. voltage at its output. By connecting an ac. load device, such a tool with an induction motor, to the output of the converter, the load may be powered from the battery.
In many instances, such a motor-alternator converter is carried in a car, truck or boat and is connected to the battery thereof so as to provide the user with mobile electrical energy for operating a 120 or 240 ac. load device at a location where utility electric service is unavailable. To avoid needless drain on the battery, it is desirable to turn off the converter motor when the load device is not being operated. In the system disclosed in the aforementioned patent, the converter motor is turned on and off automatically whenever the load device is turned on and off by a switch associated with the load device. That prior system not only required that relay contacts be disposed in the ac. current path where they were subject to arcing and pitting, but also required that initial dc. current pass in series through the dc. motor as well as the load and alternator to create the start-up signal for the motor control.